1. Field of the Invention
The present invention relates to light wave manipulating devices and, in particular, relates to filtering devices that are capable of selectively attenuating an input light beam according to wavelength such that a relatively steep attenuation curve is realized.
2. Description of the Related Art
Telecommunication networks increasingly rely on the manipulation, transmission, and detection of electromagnetic waves, or light, to provide information carrying channels with increased capacity. A typical optical channel may utilize a light source to provide a modulated light beam, a light detection device to demodulate the light beam, and a fiber optic cable to provide a beam path.
To increase the information carrying capacity of telecommunication networks, light having a plurality of wavelength components is transmitted along the cable such that each wavelength component acts as a separate channel. Since it is desirable to maximize the number of channels, the components usually have a small wavelength separation.
To further increase the information carrying capacity, light waves may be simultaneously transmitted along a single cable in opposite directions. One of the light waves includes a first plurality of desired wavelength components and the other of the light waves includes a second plurality of desired wavelengths. The wavelengths of the first wavelength components are usually interleaved between the second wavelength components.
Since the light waves are attenuated as they travel along the fiber optic cable, light amplifying stages are usually positioned along the beam path. Each stage typically includes an active medium that is optically pumped by electrically driven pump sources.
As the light waves travel along the cable, they often degrade due to cross talk among the channels and accumulate noise which introduces unwanted wavelength components into the channels. If allowed to enter the amplifying devices, the unwanted wavelength components are amplified along with the desired wavelength components. The unwanted wavelength components may limit the ability of light detection devices to detect individual desired wavelength components.
To reduce the problems of the unwanted wavelength components, a light filtering device is usually positioned in front of each light amplifying device. Ideally, the light filtering device completely blocks the unwanted wavelength components without attenuating the desired wavelength components. However, since light filtering devices known in the art have a limited ability to block the unwanted components without attenuating a substantial amount of the desired components and since the wavelengths of the wanted and desired wavelength components are often relatively close to each other, such light filtering may not provide an acceptable signal to noise ratio.
From the foregoing, therefore, it will be appreciated that there is a need for an improved light filtering device for filtering a light wave. In particular, the device should have improved filtering characteristics that allow it to simultaneously block unwanted wavelength components and pass desired wavelength components such that an improved signal to noise ratio is realized.
The aforementioned needs are satisfied by the present invention which, according to one aspect, is a light filtering assembly for filtering an input beam of light having a plurality of desired wavelength components and a plurality of unwanted wavelength components. The assembly comprises an input section disposed in the path of the input beam. The input section divides the input beam into a plurality of polarized beamlets that travel along a corresponding plurality of spatially separated beam paths. The plurality of polarized beamlets comprises (a) a plurality of desired beamlets corresponding to the desired wavelength components and (b) a plurality of unwanted beamlets corresponding to the unwanted wavelength components. The assembly further comprises a filter section disposed in the beam paths so as to receive the desired beamlets from the filter section. The filter section attenuates the unwanted beamlets and passes the desired beamlets. The assembly further comprises an output section disposed so as to receive the desired beamlets from the filter section. The output section spatially combines the desired beamlets so as to provide a filtered output beam comprising the desired wavelength components of the input beam.
Another aspect of the present invention is a method of filtering an input beam of light having a plurality of desired wavelength components and a plurality of unwanted wavelength components so as to provide a filtered output beam of light comprising the desired wavelength components. The method comprises dividing the input beam into a plurality of polarized beamlets that travel along spatially separated beam paths. The plurality of polarized beamlets comprise (a) a plurality of desired beamlets corresponding to the desired wavelength components and (b) a plurality of unwanted beamlets corresponding to the unwanted wavelength components. The desired beamlets are separated from the unwanted beamlets and then combined so as to provide the filtered output beam.
Yet another aspect of the present invention is a light manipulating assembly for manipulating an input beam of light having a plurality wavelength components so as to provide an output beam of light. The assembly comprises an input section disposed in the path of the input beam. The input section divides the input beam into a first plurality of polarized monochromatic beamlets that travel along a corresponding plurality of spatially separated beamlet paths. The assembly further comprises a beamlet manipulator disposed in the beamlet paths so as to manipulate at least one of the first plurality of polarized beamlets in a spatially dependent manner. The beamlet manipulator provides a second plurality of polarized beamlets. The assembly further comprises an output section disposed so as to receive the second plurality of polarized beamlets exiting the beamlet manipulator. The output section constructs the output beam from the second plurality of polarized beamlets.
In one embodiment, the first plurality of polarized beamlets comprises (a) a plurality of desired beamlets corresponding to a plurality of desired wavelength components of the input beam and (b) a plurality of unwanted beamlets corresponding to a plurality of unwanted wavelength components of the input beam. The second plurality of polarized beamlets comprises the plurality of desired beamlets. The beamlet manipulator comprises a filter section which attenuates the unwanted beamlets and passes the desired beamlets. The filter section comprises an opaque material having a plurality of apertures and is disposed so that the plurality of desired beamlets are aligned with the plurality of apertures and the plurality of unwanted beamlets are not aligned with the plurality of apertures. The output section spatially combines the desired beamlets exiting the filter section so as to construct the output beam which comprises the desired wavelength components of the input beam.
Another aspect of the present invention is a light filtering system for filtering a first and second input beam of light having respective first and second pluralities of desired wavelength components and respective first and second pluralities of unwanted wavelength components. The system comprises an input section disposed in the paths of the first and second input beams. The input section divides the first and second input beams into respective first and second pluralities of polarized beamlets that travel along respective first and second pluralities of spatially separated beam paths. The first and second pluralities of polarized beamlets comprise (a) respective first and second pluralities of desired beamlets corresponding to the desired wavelength components of the first and second input beams and (b) respective first and second pluralities of unwanted beamlets corresponding to the unwanted wavelength components of the first and second input beams. The system further comprises a filter section disposed in the first and second beam paths. The filter section attenuates the first and second pluralities of unwanted beamlets and passes the first and second pluralities of desired beamlets. The system further comprises an output section disposed so as to receive the first and second pluralities of desired beamlets from the filter section. The output section spatially combines the first plurality of desired beamlets so as to provide a first filtered output beam that comprises the desired wavelength components of the first input beam. The output section spatially combines the second plurality of desired beamlets so as to provide a second filtered output beam that comprises the desired wavelength components of the second input beam.
From the foregoing, it should be apparent that light dispersing assembly of the present invention is able filter the input beam such that the filtered output beam is substantially devoid of the unwanted wavelength components of the input beam. Furthermore, the light dispersing assembly is able to pass the desired wavelength components with high throughput efficiency. These and other objects and advantages of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings.